Dehydration is one of the most common conditions encountered in pediatric emergency departments among children less than 18 years of age, accounting for nearly 500,000 visits in the United States annually. Determining dehydration and its severity in infants, children, adolescents, or adults, is a procedure that may be frequently encountered in clinical and acute care settings. In some cases, it is necessary to accurately and quickly assess hydration and perfusion status of a patient so that a plan for patient care can be immediately determined and administered.
Typically, dehydration is evaluated visually and/or manually by a clinician, e.g., measuring blood pressure and heart rate, observing for sunken eyes, pinching a patient's skin to evaluate elasticity, pressing on a capillary bed and releasing to assess a change in coloration as a function of time. For example, a clinician may apply pressure to a fingernail or toenail of the patient until the region under the fingernail or toenail blanches. This indicates that blood has been forced from the capillary bed below the nail. The clinician then releases the pressure and measures the time required for the region to regain its original color. This time is referred to as a capillary refill time. Besides requiring valuable time of a skilled physician, such manual tests only provide qualitative information about a patient's degree of dehydration or vascular functioning.